In recent years, there has been a demand for compatibility of low rolling resistance and wet grip performance in pneumatic tires for passenger vehicles. In addition, there has been a demand for an improvement in wear resistance in order to extend tire life. In particular, rubber compositions that focus on wear resistance have been used in pneumatic tires for recreational vehicles (hereinafter, referred to as RVs) since such tires receive a large load from RVs. However, in recent years, a labeling (a display method) system has been initiated by JATMA (Japan Automobile Tyre Manufacturers Association), and both high-level compatibility of low rolling resistance and wet grip performance and improvements in the low rolling resistance and wet grip performance of pneumatic tires for RVs have been demanded.
In the related art, it is known that silica is blended with rubber compositions that constitute tread portions of pneumatic tires in order to enhance the balance between low rolling resistance and wet grip performance. However, in comparison with carbon black, the reinforcing property of silica with respect to rubber is low, there is a tendency for the wear resistance thereof to be insufficient, and it is difficult to improve low rolling resistance and wet grip performance while ensuring the high level of wear resistance that is required in RVs.
For example, Japanese Patent No. 4788843 describes that rolling resistance and grip performance are improved by a rubber composition, in which from 50 to 90 wt. % of a silica with a BET (Brunauer, Emmett and Teller) specific surface area of from 50 to 210 m2/g, from 35 to 80 parts by weight of a filler, which includes carbon black, and from 1 to 20 parts by weight of an aromatic modified terpene resin are blended with 100 parts by weight of a rubber component that is made from from 75 to 95 wt. % of natural rubber and styrene-butadiene rubber, and from 5 to 25 wt. % of a butadiene rubber that includes from 1 to 20 wt. % of syndiotactic-1,2-polybutadiene. Although, an effect of improving the rolling resistance and grip performance is found in this rubber composition, it is difficult to ensure the wear resistance that is required in pneumatic tires for RVs.